The solution for me:
First we did this;
- Stop all services
- Run the following queries in order:
delete from dbo.PendingNotifications
delete from dbo.SubscriptionTags
delete from dbo.Subscriptions
- Start Services.
The problem was still present. Then we did this:
Admin -> Settings - NTA settings - Applications and Service ports
Click on top "Monitor recommended ports" (which will remove duplicates from DB)
Problem solved.